In prior art, a method for producing gypsum fiber boards by the so-called Siempelkamp process is known for example from the publication DE. 2 257 827. According to this process, a dry mixture of fibers and the mineral binder calcium sulfate hemi-hydrate is spread uniformly onto a continuously moving conveyor belt. Hydration water is added by netting the dry mixture before passing it through a continuously working hydraulic press in order to form an endless board which subsequently may be cut into a plurality of separate pieces. The hydration water is added to the dry mixture before compression of the latter and is absorbed by means of vacuum applied to the fiber gypsum mixture whereby a large portion of the water which remains in the endless compressed board still reacts with the plaster. After the setting process is completed, the boards are dried and are supplied to further finishing stages, e.g., for grinding, further cutting, stacking, etc.
Today with the Siempelkamp process it is only possible to form gypsum fiber boards having a thickness of up to 19 mm at the maximum. Basically, the board thickness is dependent on the mass and the pouring height of the mixture of fibers and calcium sulfate hemi-hydrate applied onto the conveyor belt. However, at a certain mass and/or pouring height of the dry mixture of fibers and calcium sulfate hemi-hydrate, the latter may no longer wetted sufficiently by the hydration water which is added prior to compression, even if the amount of water is further increased. This means that sometimes dry material remains on the conveyor belt after pressing which is not incorporated into the plaster board to be produced.
In prior art, a solution for increasing the thickness of a board produced on a Siempelkamp production plant above the limit of 19 mm has not yet been found. As already mentioned above, neither the increase of water to be added nor any modifications to the machines used for the above described Siempelkamp production process have rendered a board thickness of more than 19 mm.